In a known pump assembly, an intermediate drive member in the form of a tappet transmits drive from a cam mechanism to a pumping plunger in order to pressurize fluid in a pumping chamber for delivery to, for example, a common rail of a diesel engine fuel injection system. The tappet reduces lateral forces applied to the pumping plunger so that generally the pumping plunger is driven by the tappet along its longitudinal axis. A known tappet is generally cup-shaped and has a cylindrical side wall portion and a base end portion. Vents are provided in the side wall portion to allow a lubricating fluid to flow from a region around the cam mechanism to a region within the tappet so that hydraulic forces do not inhibit free movement of the tappet within a tappet bore.
However, the edges of such vents in the side wall portion can be susceptible to excessive wear because contact between the tappet and tappet bore is intensified at the edges. In order to alleviate such wear, the edges may be chamfered, but such chamfering increases manufacturing costs. Secondly, the tappet tilts, albeit to a relatively small degree, with respect to the axis of the pumping plunger and the edges of the vents, chamfered or otherwise, hinder free rotation of the tappet in the bore when the tappet is tilted. Free rotation is desirable to distribute loading and wear between a lower surface of the tappet and a surface of the cam mechanism. Thirdly, the vents may become partially obscured in use in the bore particularly when the tappet is located towards its maximum range of movement within the bore. If the vents become obscured, fluid flow through the vents is restricted.